Is it confirmed that the new haste ability/spells will be 30%? I'm trying to figure out where you came up with that number for samba. Also, job ability haste caps at 25% so your response makes no sense at all.

haste samba II with 20% JA haste would open up some interesting job combo combinations in pts.

If by this, you mean get rid of the BRD, then you're right. 30% Haste 2, 25% Gear haste and 20% JA haste from samba 2 would put you at 75% delay reduction.

Unfortunately, this means that anyone with more than 20% dual-wield is losing out. H2H jobs with higher than Martial Arts 2 are losing out. Anyone using Hasso or Last Resort is losing out.

So there are places where this would be useful, eg on mobs weak to piercing that you want to bring DRGs for, DRGs would love to come DRG/WAR and benefit from (almost) capped haste (capped if samba II was 25%). Other DDs could have other options available, like using Seigan for more damage mitigation instead of hasso, or for when /NIN is needed for shadows, but not useful for DW.

So yeah, it opens up a new role in parties for DNC rather than bringing a BRD, but then DNC's steps have to equate to the other songs that you'd get from a BRD, or the DNC's own damage needs to bridge the gap that you're losing from the other DDs having lower acc/att.

Well, they've said that they're going to adjust Dual Wield in September so that it no longer causes TP decrease past the 80% delay cap. With that announcement and the introduction of all the new sources of magic Haste in the last update (and future updates - Hastega II), I think they want capped delay to be a standard for all parties instead of just parties patient enough to hold out for a bard. If SE manages to fix Geomancer so that it can actually maintain a Luopan without an ergon weapon, their Indi-Haste has a lot of potential and their Defense Down debuff is more useful than minuets. Combine that with reworked Avatar's Favor and Hastega II (which make SMN a more viable buffer, hopefully), and you have a lot more options for meleeburns. Red Mage is currently a desirable party member for PLD + RNG setups, but if they let the job cast Temper on party members it would be similarly desirable as SMN and GEO.

I foresee Bard becoming much less useful in the next few months. I personally have all the BRD RMEs and currently do VD fights with some regularity, but I'm wondering if the ideal strategy in the future will involve just having me sing before a VD fight and drop for a more useful job. 9-10 minutes of Madrigals and Minuets while also getting Indi-Haste and a defense or evasion down debuff on the target seems like a better deal, and we're one GEO fix away from that being a reality.

Also, as far as losing out on DW, we already cap delay with Haste Samba and Haste II even without all our dual wield gear:
* 256 Gear + 307 Haste II + 101 Haste Samba = 664/1024
With that much haste you need 43% Dual Wield to cap delay, which would be Patentia Sash, Suppa, and Charis necklace. No reason to wear Charis body +2 (or you can keep wearing it and switch to Windbuffet and Steelflash/Bladeborn).